Effect of the Fe/Co Ratio on Electrocatalytic OER Activity of Cofe-LDH

Solar hydrogen production through photocatalytic or photoelectrochemical water splitting has been considered as a promising route for overcoming the current global reliance on fossil fuels. Within these processes, oxygen evolution reaction requires a large overpotential due to its slow reaction kinetics. Therefore, achievement of efficient OER catalysis using abundant elements has been highly demanding challenge and understanding of the reaction mechanism of OER is important for a rational design of active catalysts. Recently, we identified that Fe 4+ acts as an intermediate species of OER on α-Fe 2 O 3 , and its efficient formation was found to be necessary to lower the overpotential [1]. Meanwhile, Fe ions incorporated into Ni and Co hydroxides have been reported to be oxidized to Fe 4+ during electrochemical anodization [2],[3], and efficient OER has been demonstrated using NiFe and CoFe layered double hydroxides (LDHs) [4]. In this study, we studied the effect of Fe addition on electrical property and OER activity of CoFe-LDH. CoFe-LDH with different ratio of Co and Fe was synthesized on FTO substrate using hydrothermal method, and its formation was confirmed by XRD measurements. Figure shows chrono amperograms of CoFe-LDH measured at alkaline conditions. As the ratio of Fe was increased up to 36%, a gradual improvement in current density and a negative shift in the onset potential were observed although further increase in Fe content was detrimental for OER activity. Notably, all the CoFe-LDH showed higher OER activity compared with both monometallic Co and Fe oxyhydroxide, indicating that coexistence of Co and Fe is beneficial for the catalyst performance. Details will be discussed in the conference. Reference [1] T. Takashima, K. Ishikawa, H. Irie , J. Phys. Chem , 2016, 120 , 24827 [2] Hans Christian Bruun Hamen, Christian Bender Koch , Inorg. Chem , 1994, 33 , 5363-5365 [3] G. Rajeshkhanna, Thangjam Ibomcha Singh, Nam Hoon Kim, Joong Hee Lee, ACS Appl. Mater. Interfaces, 2018, 10 , 42453-42468 Figure 1